Corn hybrid P725

ABSTRACT

A hybrid corn line having the designation P725, produced by crossing two maize inbreds, Qx47 and Zx23. P725 imparts a high oil level in the grain of certain male sterile hybrids when used as a pollinator. P725 is characterized by excellent seedling vigor in cold soil tests and excellent productivity in TC BLEND® Seed Corn Products of medium to late season adaptability. This invention thus relates to the seeds, plants and plant parts of P725 and its components, to plants regenerated from tissue culture of the plants of P725, to a method of producing P725, and to a method for producing high oil grain using P725 as a pollinator.

FIELD OF THE INVENTION

This invention is in the field of maize breeding. Specifically, thisinvention relates to a novel corn hybrid having the designation P725.

BACKGROUND OF THE INVENTION

Principles of Conventional Plant Breeding

Most of the commercial corn produced in the United States is producedfrom hybrid seed. The production of hybrid seed first requires thedevelopment of elite corn inbred lines that possess good combiningability to produce agronomically superior hybrids. The majority ofhybrid seed produced in the United States is of the single cross type,wherein two inbred lines are intermated, or crossed, to produce what istermed seed of an F₁ single cross hybrid. This seed is then sold tocommercial grain growers who plant the seed and harvest the secondgeneration, or F₂ grain, for use on farm or for commercial sale.

The production of conventional single cross hybrid seed involvescontrolling the direction of pollination from one inbred to the other toassure the production of predominantly hybrid (cross pollinated) seed.Typically, directed pollination is accomplished by interplantingseparate rows of female corn plants with male corn plants. The femalecorn plants that are male sterile may be produced by genetic mechanismswhich render the corn tassel or pollen nonfunctional or by detasselingthe plants in the field.

The development of corn hybrids requires the development of homozygousinbred lines, the crossing of these lines, and the evaluation of thecrosses. Pedigree breeding, backcross conversion and recurrent selectionbreeding methods are used to develop the inbred lines from breedingpopulations. These breeding methods combine desirable traits from two ormore inbred lines or various broad-based populations into breeding poolsfrom which new inbred lines are developed by inbreeding or random matingand selection of desired phenotypes. The new inbreds are crossed withother inbreds and the resulting hybrids are evaluated to determine whichhave commercial value and agronomic usefulness.

The objective of typical plant breeding is to develop a hybrid withdesirable traits such as resistance to diseases and insects, herbicidetolerance, tolerance to heat and drought, reduction of time to cropmaturity, and improved agronomic quality. Because many crops areharvested mechanically, uniformity of plant characteristics such asgermination time, stand establishment, growth rate, and fruit/seed sizeare also desirable.

The problem with conventional breeding techniques is that there areseveral grain quality traits, such as high oil concentration, thatcannot readily be obtained in a high-yielding single cross hybrid. Onesolution to this problem has been proposed by Bergquist et al. in U.S.Pat. Nos. 5,704,160 and 5,706,603, incorporated herein by reference. Aprimary aspect of this method, known as the TOPCROSS® Grain ProductionSystem, is the interplanting of a pollinator corn plant possessing thecharacteristics for significantly increasing oil level in the resultinggrain, with a male sterile hybrid corn plant. The resulting grainpossesses an oil concentration much higher than would be expected forself- or cross- pollination of the fertile version of the hybrid cornplant.

In practice, the seed of the pollinator with improved grain qualitytraits is blended in small amounts with seed of an elite male sterilegrain parent hybrid, but with sufficient pollinator seed to permitabundant pollen production for fertilization of the male sterile grainparent hybrid. The relatively low ratio of pollinator seed to malesterile grain parent seed (less than one pollinator plant to every threegrain parent plants) takes advantage of the higher grain yield potentialof the elite grain parent hybrid while assuring a sufficient populationof pollinator plants to pollinate the male sterile grain parent plants.

Critical to the success of the TOPCROSS® Grain Production System is theuse of a pollinator capable of enhancing the grain quality traits of theF₁ grain. P725 was developed for this purpose. The present invention,when used as a pollinator, imparts high oil concentration to theresulting F₁ grain without significant loss of yield.

SUMMARY

According to the invention, there is provided a novel corn hybrid,designated P725, that when used to pollinate an elite male sterilehybrid grain parent, produces commercial grain exhibiting improvedquality grain traits, including high oil.

P725 is a medium-late flowering hybrid, broadly adapted to the corngrowing areas of the Southern and Central United States. P725 hasexpressed high oil and excellent plant vigor and productivity.

The invention thus relates to the seeds, plants and plant parts of P725;to tissue culture comprising regenerable cells of a plant part of P725;to plants regenerated from regenerable cells of the tissue culture ofP725; to corn plants having substantially all the phenotypic, genotypicand/or physiological characteristics of P725; to the method of producingP725; to grain or seed produced by crossing P725 with a different cornplant wherein the resulting progeny have one-half the nuclear genotypeof P725; to seed blends of P725 and male sterile corn hybrids; to amethod of producing high oil grain using P725 as a pollinator in a TCBLEND® Seed Product; to the parental lines of P725; and to corn plantsproduced or derived from P725 seed wherein the corn plants have theability to impart high oil or other grain quality traits to the F1 grainwhen these P725-derivatives are used in the TOPCROSS® Grain ProductionSystem.

DEFINITIONS

In the description that follows, a number of terms are used. In order toprovide a clear and consistent understanding of the specification andclaims, including the scope to be given such terms, the followingdefinitions are provided:

Combining Ability. The ability of a genetic strain, when crossed withanother strain, to produce a high proportion of desirable individuals.

Endosperm. The nutritive tissue formed within the embryo sac in seedplants. It commonly arises following the fertilization of the diploidpolar nucleus by one male sperm.

Express. To manifest a genetic character trait.

F₁. The first generation of a cross.

F₂. The second filial generation obtained by self-fertilization orcrossing inter se of F₁ individuals. Subsequent generations are F₃, F₄,F₅, etc.

Genotype. The fundamental genetic constitution of an organism.

Grain. Mature corn kernels produced by commercial growers for purposesother than growing or reproducing the species.

Grain Parent. Male sterile, elite hybrid that comprises a large majorityof the plants in the TOPCROSS® Grain Production System.

Grain Quality Trait. Any attribute of grain that is of commercial value.Such traits relate to the intermediate or final use of grain and includebut are not limited to the quantity or quality of oil, protein, starch,pigmentation, and fiber found in corn grain. Such traits also encompassphysical attributes of the grain itself, such as grain texture, size, orhardness, among others. Certain of these compositional or physicalattributes of grain correlate with functional attributes as well whichare of commercial importance, such as susceptibility to breakage andspoilage, among others.

Homozygous. A genetic condition existing when identical alleles resideat corresponding loci on homologous chromosomes.

Hybrid. (1) The progeny of a cross fertilization between parentsbelonging to different genotypes. (2) The first generation offspring ofa cross between two individuals differing in one or more genes. (3) Ahybrid is the result of a cross between two or more components.

Inbred or Inbred Line. A substantially homozygous individual, variety orline produced by continued inbreeding. In plant breeding a nearlyhomozygous line usually originates by continued self-fertilization,accompanied by selection.

Kernel. The corn caryopsis comprising a mature embryo and endospermwhich are products of double fertilization.

Line. (1) A group of individuals from a common ancestry. (2) A narrowlydefined group that is a variety.

Male Sterile. A condition in which pollen is substantially absent ornon-functional in flowering plants.

Percent Oil. The oil concentration of a corn kernel, typicallydetermined at 0% moisture.

Phenotype. (1) Physical or external appearance of an organism ascontrasted with its genetic constitution (=genotype); (2) a group oforganisms with similar physical or external makeup; (3) the observedcharacter of an individual without reference to its genetic nature.

Pollen grain. A microspore in flowering plants that germinates to formthe male gametophyte which contains three haploid nuclei. One of thesefertilizes the ovum, a second fuses with the two polar nuclei to formthe triploid endosperm, and the third degenerates once doublefertilization has been accomplished.

Pollinators. Male fertile corn plants used to pollinate male sterilehybrid corn plants in order to produce a Grain Quality Trait in theresulting F1 grain.

Population. In genetics, a community of individuals which share a commongene pool.

Seed. Mature corn kernels produced for the purpose of propagating thespecies.

Single Cross. A cross between two different genotypes, each of which maybe an inbred or synthetic.

Synthetic (Population). A genetically heterogeneous collection of plantsof known ancestry created by the intermating of any combination ofinbreds, hybrids, varieties, populations, races or other synthetics.

Synthetic Hybrid. A hybrid in which one or more genotypes used to makethe hybrid is a synthetic.

TC BLEND®. A registered trademark of E.I. du Pont de Nemours and Companyfor a physical mixture of two or more types of seed utilized in theTOPCROSS® Grain Production System.

Test Weight. The measure of the weight of the grain in pounds for abushel volume.

TOPCROSS®. A registered trademark of E.I. du Pont de Nemours and Companyfor the TOPCROSS® Grain Production System.

Yield (Bushels/Acre). The yield of corn in bushels/acre is the number ofbushels of grain at harvest per acre, where one bushel is equal to 56pounds adjusted to 15.5% moisture.

DETAILED DESCRIPTION OF THE INVENTION

P725 is a high oil single cross hybrid having superior agronomiccharacteristics and the ability to impart desirable grain quality traitsto grain when used as a pollinator in the TOPCROSS® Grain ProductionSystem. P725 is adapted over a wide area of the Southern and Centralregions of the U.S. corn belt. P725 can be used advantageously in TCBLEND® Seed Corn Products with grain parents from approximately 112-118relative maturity.

P725 is produced by crossing proprietary corn inbred lines Qx47 andZx23. Either parent line may be used as the female parent or the maleparent. P725's inbred parents have large, highly branched tassels.

Although P725's primary use would be as a pollinator in the TOPCROSS®Grain Production System with blends of medium to late maturing cornhybrid male sterile grain parents, it is also an acceptable parent to becrossed with other high oil pollinators to develop derived pollinators,for example by crossing to earlier or later pollinators for expandingthe use of its genetics to wider maturity grain parents.

Comparison of P725 to Synthetic Hybrid LP57.1

LP57.1 is a synthetic hybrid described in U.S. Pat. No. 5,824,854. Asshown in Table 1, the timing of P725 flowering is very similar toLP57.1. However, P725 has a shorter interval between the 10% and 90%pollen shedding dates, which is as expected, since LP57.1 is a synthetichybrid which tends to spread out the shedding period.

TABLE 1 Average of 1998-1999 Flowering Observations on the Number ofDays from Planting to 10%, 50% and 90% of the Plants Shedding Pollen.(1998: 21 locations; 1999: 28 locations; 2 replicates/location)Pollinator 10% Shedding 50% Shedding 90% Shedding LP57.1 65.2 67.4 69.5P725 65.7 67.6 69.4

When used as a pollinator, P725 produces kernels very similar to thoseproduced using LP57.1 as the pollinator, with comparable oilconcentration and test weight. P725 may have improved plant vigor overLP57.1, as suggested by cold soil germination tests (see Table 2) andyield measurements on the pollinator plants themselves (see Table 3).

TABLE 2 1999 Field Emergence Observations, Williamsburg IA, With a VeryEarly Planting Date (March 31, 1999) Providing Cold Soil Conditions. (3replicates) Interval from 1st Plant to Pollinator Emergence 10 PlantsEmerged LP57.1 45% 7 days P725 75% 2 days

TABLE 3 1998 Yield Trial Results, Pollinators per se, Grown in 2-row ×19 ft. Plots in Three Midwest Locations (3 replicates/location)Pollinator Yield (bu/A) Harvest Moisture (%) LP57.1 93 18.3 P725 14518.6

EXAMPLES OF USING P725 AS A POLLINATOR

Strip test trials were conducted by Holden's Foundation Seeds, L.L.C. inthe summer of 1998 to compare the characteristics of grain produced fromvarious hybrids rendered male sterile and pollinated by P725 (“High OilCorn Grain”) with the characteristics of grain produced from the samehybrids in their fertile state and not pollinated by P725. As Table 4shows, the average oil concentration of the High Oil Corn Grain was 3.1percentage points higher on a dry basis (db) than the average oilconcentration of grain from the corresponding fertile hybrids. Grainmoisture at harvest was 0.2 percentage points higher, test weight was2.0 lb/bu lower, and protein was 0.2 percentage points lower in the HighOil Corn Grain compared to the grain from the corresponding fertilehybrids.

TABLE 4 1998 TOPCROSS ® Grain Production System Strip Test Results UsingP725 as Pollinator Across a Range of Hybrid Grain Parents AbsoluteIncrease or Decrease Over the Mean Value for Grain Produced from theSelf- and Sib-pollinated Grain Parents Grain Moisture Oil Protein atHarvest Test Weight Concentration Concentration (%) (lb/bu) (% at 0%moisture) +0.2 −2.0 +3.1 −0.2

Table 5 presents 1998 strip test data for a single grain parent hybrid(LH200SDms×LH185) pollinated by P725 at a number of locations. As Table5 shows, the average level of oil in grain arising from LH200SDms×LH185pollinated by P725 at seventeen locations was 7.5%.

TABLE 5 1998 Strip Test Data Using LH200SDms × LH185 as the Grain ParentGrain Moisture Grain at Test Yield Harvest Weight Oil Protein Starchbu/acre % lb/bu % at 0% moisture 162 17.4 54.6 7.5 8.4 67.6 Number of 1818 15 17 17 17 locations

Table 6 presents 1998 strip test data for the grain parent hybridLH200SDms×LH185 pollinated by P725 compared to data for the fertilecheck (LH200×LH185). Grain arising on the male sterile grain parentpollinated by P725 (“High Oil Corn Grain”) exhibited, on average, 7.6%oil or 173 percent of the oil concentration in the grain produced by thefertile check.

TABLE 6 1998 TOPCROSS ® Grain Production System Strip Test Data AveragedOver A Number of Locations Grain Moisture Grain at Test Yield HarvestWeight Oil Protein Starch bu/acre % lb/bu % at 0% moisture Grain 17318.1 56.0 4.4 8.2 71.7 Parent Fertile Check (GP) High Oil 158 18.0 54.57.6 8.3 67.2 Corn Grain High Oil 91.3 99.9 97.3 173 101 93.7 Corn Grainas % of GP Number of 11 11 10 9 9 9 locations

Table 7 presents data comparing the performance of TC BLEND® SeedProducts using the same grain parent, LH200SDms×LH185 but either LP57.1or P725 as the pollinator component. These data indicate that in aside-by-side comparison, the P725 seed blend is higher yielding, withthe same grain traits as the LP57.1 blend.

TABLE 7 1998 TOPCROSS ® Grain Production System Strip Test Results forLP57.1 versus P725 Used in TC BLEND ® Seed Products with LH200SDms ×LH185. Yield Moisture Oil Test Wt. Seed Blend (bu/A) (%) (%, db)(lbs/bu) LH200SDms × LH185 + 157 16.9 7.7 55.1 LP57.1 LH200SDms ×LH185 + 165 17.3 7.6 55.2 P725 No. of Locations 15 15 14 11

Applicant has made available to the public without retriction a depositof at least 2500 seeds of maize hybrid P725 with the American TypeCulture Collection (ATCC), Rockville, Md. 20852, ATCC Deposit No.PTA-2977. Parental seed stocks of Qx47 and Zx23 have also been madeavailable to the public without restriction from a deposit of at least2500 seeds of each population with the American Type Culture Collection(ATCC) under Deposit No. PTA-2973 for Qx47 and No. PTA-2979 for Zx23.

The seeds deposited with the ATCC were taken from the same depositsmaintained by Holden's Foundation Seeds, L.L.C., 503 S. Maplewood Ave.,P.O. Box 839, Williamsburg, Iowa 52361 since prior to the filing date ofthis application. The deposits will be maintained in the ATCCdepository, which is a public depository, for a period of 30 years, or 5years after the most recent request, or for the enforceable life of thepatent, whichever is longer, and will be replaced if it becomesnonviable during that period.

Although the foregoing invention has been described in some detail byway of illustration and examples for purposes of clarity andunderstanding, it will be obvious that certain modifications andalternative embodiments of the invention are contemplated which do notdepart from the spirit and scope of the invention as defined by theforegoing teachings and appended claims.

What is claimed is:
 1. A hybrid corn line designated P725, for which arepresentative sample of seeds has been deposited under ATCC AccessionNo. PTA-2977.
 2. A hybrid corn seed designated P725, a representativesample of which has been deposited with the ATCC under Accession No.PTA-2977.
 3. A hybrid corn plant produced by the seed of claim
 2. 4.Pollen of the hybrid corn plant of claim
 3. 5. A tissue culturecomprising regenerable cells of the hybrid corn plant of claim
 3. 6. Acorn plant regenerated from regenerable cells of the tissue culture ofclaim
 5. 7. A corn plant having substantially all the morphological andphysiological characteristics of the hybrid corn plant of claim
 3. 8. Acorn plant having all the phenotypic, genotypic and physiologicalcharacteristics of the hybrid corn plant of claim
 3. 9. A method forproducing a hybrid corn seed comprising the steps of a) planting inpollinating proximity seeds of corn inbred lines Qx47 (ATCC AccessionNo. PTA-2973) and Zx23 (ATCC Accession No. PTA-2979); b) cultivatingcorn plants resulting from the planting until the time of flowering; c)emasculating the flowers of the plants of either inbred line Qx47 orZx23; d) allowing cross pollination to occur between the inbred lines;and e) harvesting seeds produced on the emasculated plants.
 10. Grainproduced by crossing a hybrid corn plant according to claim 3 withanother, different corn plant.
 11. Seed produced by crossing a hybridcorn plant according to claim 3 with another, different corn plant. 12.A seed corn blend comprising a mixture of male sterile hybrid corn seedand the hybrid corn seed of claim
 2. 13. Corn grain produced by theprocess of: (a) planting, in pollinating proximity, the hybrid corn seedof claim 2 and seeds of a male sterile corn hybrid; (b) cultivating cornplants resulting from the planting; (c) allowing the P725 corn plants topollinate the male sterile hybrid corn plants; and (d) harvesting theresulting corn grain from all plants.
 14. Corn seed designated Qx47, arepresentative sample of which has been deposited with the ATCC underAccession No. PTA-2973.
 15. Corn seed designated Zx23, a representativesample of which has been deposited with the ATCC under Accession No.PTA-2979.
 16. A corn plant produced from a seed of claim 2 and havingthe ability to impart desirable grain quality traits to grain when usedas a pollinator plant in the TopCross® Grain Production System.
 17. Acorn plant produced from a seed of claim 2 having the ability to imparta high oil level to grain when used as a pollinator plant in theTopCross® Grain Production System.
 18. A corn plant derived from a seedof claim 2 and retaining the ability to impart a high oil level to grainwhen used as a pollinator in the TopCross® Grain Production System.